The present invention relates to a television receiver compatible with standard/high definition television signals capable of receiving and reproducing television signals of two different systems, i.e., the standard television signal and the high definition television signal.
In response to the demand for higher picture quality of television receivers, a high definition television system is being newly developed in recent years. The high definition television system was proposed by Nippon Hoso Kyokai (NHK) in advance of others in the world. In the high definition television system thus proposed, the aspect ratio of the screen is 16 : 9 (or 5 : 3) and the number of scanning lines is 1125, resulting in a system different from the current standard television system (i.e., the NTSC system having the aspect ratio of 4 : 3 and the number of scanning lines equivalent to 525).
As a broadcast service form of this high definition television, the high-vision satellite transmission system (hereafter referred to as MUSE) for transmitting bandwidth-compressed signals by using a broadcasting satellite has been developed. The principle, signal format and schematic configuration of the receiving apparatus of this MUSE are described in "An HDTV Broadcasting System Utilizing a Bandwidth Compression Technique-MUSE", Yuichi Ninomiya et al., IEEE Trans., Vol. BC-33, No. 4, pp. 130-160, December 1987. Upon the start of such high definition television broadcasting, the receiving apparatus is requested to be capable of receiving signals of the two systems, i.e., the conventional standard television signal and the MUSE signal. In response to such a request, several processing methods have heretofore been devised. For example, Japanese Patent Applications JP-A-59-70369 and JP-A-59-104866, each of which discloses a conversion system between the high definition television system and the standard television system, JP-A-61-206380, JP-A-61-206381, JP-A-63-26172 and JP-A-63-263783, each of which discloses a method for eliminating the difference in aspect ratio, and JP-A-62-206977, which discloses an image memory commonly used for processing of both systems, can be mentioned.
Further, examples of known literature relating to the technical field of the present invention will now be described. U.S. Pat. No. 4,733,300 issued on Mar. 22, 1988 to Sugiyama et al. discloses a circuit for converting an interlace television signal to a noninterlace (or sequential scanning) television signal. U.S. Pat. No. 4,733,297 issued on Mar. 22, 1988 to Katsumata et al. discloses a circuit for applying motion-adaptive processing to video signals. Japanese Patent Application laid-open No. JP-A-58-81386 filed by Miura et al. on Nov. 10, 1981, discloses a system in which the number of scanning lines of the standard NTSC signal is converted to become twice so as to attain compatibility with the high definition television signal. Japanese Patent Application laid-open No. JP-A-61-267469 field by Nagashima on May 21, 1985, discloses a system in which two different television systems are made common in number of scanning lines so as to attain compatibility.
In the above described related techniques, consideration is not given to the fact that the MUSE signal is also received and processed in the so-called double speed television system in which the standard television signal is displayed after its interlace scanning has been converted into sequential scanning. The following problems are thus posed.
(1) In case a 16:9 high definition display is used:
Since the MUSE signal is subject to complete decode processing, the scale of the processing circuit increases, resulting in a higher cost.
(2) In case a 4:3 standard display is used:
Since the MUSE signal is converted to the standard television signal, significant lowering in picture quality is caused.